According to the Ministry Calendar it will be March 16-20. Know that your own school board can ask to have it changed, although I don't think many do. Ours always follows the ministry guidelines. At least you have a start!
York Region is the 16-20th also - it's late this year which has me a little more worried about how busy the parks will be! We used to take the first and second week of March to go and the first week was always half of the crowds. Now we will be there mid March - ugh!